A hub firm is an agent that connects retailers to marketplace structures with the aim of selling products to final customers. Although social media is a decisive driver of consumer outcomes, it is unclear how a hub firm's earned and owned social media influences retailers' sales. Drawing on social identity theory, the authors propose a theoretical model that addresses the effects of blog comments, Facebook comments, fan following, and organic search sources (from a hub) on retailers' performance. In addition, the authors suggest that marketplace organic search moderates these main effects. Building on 4107 observations from 615 individual retailers across 26 months, the proposed model reveals that blog and Facebook comments, fan following, and hub organic search increase retailers' sales. Moreover, the results support the moderating role of marketplace organic search in amplifying these effects. Specifically, the effect of the interaction between marketplace organic search and hub organic search is significantly greater than that of the other examined interactions with Facebook or blog comments.